Arthur T Knackerbracket has processed the following story:
It's not easy making green. For years, scientists have fabricated small, high-quality lasers that generate red and blue light. However, the method they typically employ—injecting electric current into semiconductors—hasn't worked as well in building tiny lasers that emit light at yellow and green wavelengths.
Researchers refer to the dearth of stable, miniature lasers in this region of the visible-light spectrum as the "green gap." Filling this gap opens new opportunities in underwater communications, medical treatments and more.
Green laser pointers have existed for 25 years, but they produce light only in a narrow spectrum of green and are not integrated in chips where they could work together with other devices to perform useful tasks.
Now scientists at the National Institute of Standards and Technology (NIST) have closed the green gap by modifying a tiny optical component: a ring-shaped microresonator, small enough to fit on a chip. The research is published in the journal Light: Science & Applications.
A miniature source of green laser light could improve underwater communication because water is nearly transparent to blue-green wavelengths in most aquatic environments. Other potential applications are in full-color laser projection displays and laser treatment of medical conditions, including diabetic retinopathy, a proliferation of blood vessels in the eye.
Compact lasers in this wavelength range are also important for applications in quantum computing and communication, as they could potentially store data in qubits, the fundamental unit of quantum information. Currently, these quantum applications depend on lasers that are larger in size, weight and power, limiting their ability to be deployed outside the laboratory.
For several years, a team led by Kartik Srinivasan of NIST and the Joint Quantum Institute (JQI), a research partnership between NIST and the University of Maryland, has used microresonators composed of silicon nitride to convert infrared laser light into other colors. When infrared light is pumped into the ring-shaped resonator, the light circles thousands of times until it reaches intensities high enough to interact strongly with the silicon nitride. That interaction, known as an optical parametric oscillation (OPO), produces two new wavelengths of light, called the idler and the signal.
In previous studies, the researchers generated a few individual colors of visible laser light. Depending on the dimensions of the microresonator, which determine the colors of light that are generated, scientists produced red, orange and yellow wavelengths, as well as a wavelength of 560 nanometers, right at the hairy edge between yellow and green light. However, the team could not generate the full complement of yellow and green colors necessary to fill the green gap.
"We didn't want to be good at hitting just a couple of wavelengths," said NIST scientist Yi Sun, a collaborator on the new study. "We wanted to access the entire range of wavelengths in the gap."
To fill the gap, the team modified the microresonator in two ways. First, the scientists slightly thickened it. By changing its dimensions, the researchers more easily generated light that penetrated deeper into the green gap, to wavelengths as short as 532 nanometers (billionths of a meter). With this extended range, the researchers covered the entire gap.
In addition, the team exposed the microresonator to more air by etching away some of the silicon dioxide layer below it. This had the effect of making the output colors less sensitive to the microring dimensions and the infrared pump wavelength. The lower sensitivity gave the researchers more control in generating slightly different green, yellow, orange and red wavelengths from their device.
As a result, the researchers found they could create more than 150 distinct wavelengths across the green gap and fine-tune them. "Previously, we could make big changes—red to orange to yellow to green—in the laser colors we could generate with OPO, but it was hard to make small adjustments within each of those color bands," Srinivasan noted.
The scientists are now working to boost the energy efficiency with which they produce the green-gap laser colors. Currently, the output power is only a few percent of that of the input laser. Better coupling between the input laser and the waveguide that channels the light into the microresonator, along with better methods of extracting the generated light, could significantly improve the efficiency.
Journal information: Light: Science & Applications
(Score: 3, Interesting) by Rosco P. Coltrane on Monday September 09, @08:17PM
Brainiac75 has you covered [youtu.be]: the man collects lasers among other things, and he finally got his hands on true yellow lasers last year.
Besides, his is a damn interesting channel too.
(Score: 2) by tangomargarine on Monday September 09, @09:20PM
Why It Was Almost Impossible to Make the Blue LED [youtube.com]
"Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
(Score: -1, Spam) by pledgeoink on Tuesday September 10, @07:37AM
(Score: 3, Interesting) by mcgrew on Tuesday September 10, @02:19PM (6 children)
Other potential applications are in full-color laser projection displays
Holograms. You could have a true 3D screen, not just binocular vision as in red/green and polarized 3D glasses, but true 3D and needing no special glasses. They had monochrome holograms in a physics course I took in the late '70s. Even with everything in the photo colored shades of red it was impressive as hell and put polarized "3D" to shame.
With computers and the correct three colors of lasers (they they may not yet have, I don't know) you could easily make holographic movies. Of course, filming would have to be done entirely in laser light.
A Russian operative has infiltrated the highest level of our government. Where's Joe McCarthy when we need him?
(Score: 2) by Freeman on Tuesday September 10, @02:37PM (1 child)
All you would need is some sort of spatial 3D recording. You don't need special recording devices to display a video on LCD/LED/OLED/etc. In fact you might could play current 3D Videos and/or 360 videos using some sort of holographic display technology. Regular 2D film styles would likely not convert well and/or just be lacking in 3D characteristics.
Joshua 1:9 "Be strong and of a good courage; be not afraid, neither be thou dismayed: for the Lord thy God is with thee"
(Score: 3, Interesting) by mcgrew on Wednesday September 11, @01:07PM
I don't see how you could convert a photograph into a hologram. In a hologram, the film just holds a moire pattern that looks like nothing in normal light.
That said, I still had movies converted to holograms in Journey to Madness [mcgrewbooks.com].
A Russian operative has infiltrated the highest level of our government. Where's Joe McCarthy when we need him?
(Score: 2) by ledow on Wednesday September 11, @07:43AM (3 children)
Those holograms can only be formed with some medium in the middle to reflect off, and that means a large space dedicated to your TV.
We already threw that space away and put things on a flat wall many years ago.
We had "holograms" in the arcades in the 80's, they never took off - it's like a VR fad cycle all over again.
And we have lasers in enough colours that full colour HD / 4K laser projectors are commodity hardware that you can go and buy today, and many places are already using them and you don't even realise - just about any museum, 3D show, observatory show, etc. are using laser projectors because they don't fade, don't need much maintenance - e.g. bulbs - and provide a consistent image), and their use comes right down to theatres, schools, sports halls and meeting rooms.
This isn't going to open up any new wave of holographic tech.
(Score: 2) by mcgrew on Wednesday September 11, @01:01PM (2 children)
Those holograms can only be formed with some medium in the middle to reflect off,
Sorry, but I don't know what you're talking about. Perhaps what Disney has to make ghosts with in their Haunted Mansion? That's not a hologram, it's a simple optical trick used on stages for centuries.
To make a hologram with photographic film, you light the subject with laser light and expose the film momentarily, without an aperture or lens, and develop the film. The resulting film will not have a photo in white light, but laser light reveals the truly three dimensional image of the photographed subject, behind the film.
For a holographic computer display, it would be constructed of red, yellow, and cyan lasers rather that those colors of LEDs as your normal LED monitor.
A Russian operative has infiltrated the highest level of our government. Where's Joe McCarthy when we need him?
(Score: 2) by ledow on Wednesday September 11, @06:09PM (1 child)
Pepper's Ghost (used in theatre, theme parks and also used on 80's hologram arcade games) requires a lot of extra space and mirrors / glass sheets.
A hologram that is in 3D space needs 3D space and a medium (usually a fogging agent). A laser, in and of itself, is invisible on its path through the air and only visible when it reflects off something to your eye.
A 2D hologram is not a hologram as we're talking about it, and has no need of a special particular-green-coloured laser.
(Score: 2) by mcgrew on Friday September 13, @07:22PM
The hologram as I saw them "in the flesh" in the late 1970s is a sheet of photographic film with a moire pattern that doesn't look like anything in normal light, but illuminate it with a laser and the film becomes not a picture, but a truly 3D image.
I had forgotten the name of Pepper's Ghost. That does indeed take a lot of room, but again, it isn't a hologram.
A Russian operative has infiltrated the highest level of our government. Where's Joe McCarthy when we need him?